Diesel engines may utilize fuel/water separators to remove water from fuel, into a reservoir, and then inject the separated fuel into the engine system. These systems aim to reduce engine degradation caused by the presence of water in the fuel. Some fuel/water separators require manual drainage of water from the reservoir. If the vehicle operator does not drain the reservoir, water may enter and cause damage to the fuel system. Other separators may include an automatic drainage system; however, regulations prohibit discarding of the separated water to the environment. Thus, some systems automatically drain the water from the reservoir to an alternate location in the exhaust system.
One example approach is shown by Ruona et al. in U.S. 2006/0277899. Therein, the water separated from the fuel is injected into an exhaust after-treatment device and eliminated as water vapor. The water is introduced, as a dose, into the after-treatment device when the stored water level in the reservoir (receiving water from the separator) reaches a predetermined level.
However, the inventors herein have recognized potential issues with such systems. For example, while such operation can dispose of the collected water, the shift in the exhaust gas composition caused by the water can affect catalyst performance. Specifically, the water can not only affect the catalyst chemistry and reactions, but it can also cool the exhaust temperature due to evaporation of the water, reducing catalyst conversion efficiency.
In one example, the issues described above may be at least partly addressed by a method comprising automatically draining the water from a diesel fuel system into an exhaust gas recirculation system. For example, water from the fuel/water separator may be returned back into the engine for disposal via the exhaust gas recirculation (EGR) system. In this way, the introduced water may mix with recirculated exhaust in the EGR system before re-entering the intake manifold for combustion.
In one example, during engine operation, water may be separated from the fuel system via a fuel/water separator and stored in a reservoir. In response to a water level in the reservoir reaching a threshold level and EGR above a minimum flow threshold, an automatic draining of the water to the EGR system may be initiated. Therein, by opening a valve, water may flow from the water reservoir into the EGR system. Based on the amount of engine dilution introduced into the EGR via the water, an amount of exhaust gas recirculated via the EGR valve may be reduced. The mixture of water and EGR may then be introduced, together, into the intake manifold for combustion in the engine. By introducing water into the intake of the engine via the EGR system, catalyst conditions can be maintained. Specifically, a temperature of the catalyst can be maintained, while also maintaining catalyst conversion efficiency and chemistry. By mixing the water with the EGR before introduction into the engine, and introducing the water via the engine intake rather than the engine exhaust, changes in catalyst chemistry caused due to water at the exhaust catalyst can also be reduced. Disposing of water in this way may also allow reduction of EGR when water is introduced. For example, once the water volume in the fuel system reaches a predetermined level and EGR flow is above a minimum flow threshold, water may be introduced. By adjusting an amount of EGR based on the amount of water introduced into the EGR system, a desired engine dilution can be provided with lower EGR while still providing NOx reduction benefits. As in EGR, the introduced water may also be used to absorb heat and reduce combustion temperatures, improving engine performance.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.